The only change is the use of table variables instead temporary tables (@ instead #).
Dapper (or anything other in the chain?) seems to somehow mix this up with parameters and returns "Must declare the table variable @t".

Is there anything wrong in my usage or is this a bug/missing feature in dapper?

Best regards,
Kc

UPDATE:

Just to clarify: @t is not a parameter to be set by dapper. @t is declared as a local table that's only existent for the currently running query. In my opinion, dapper should not distinguish between any type of table, be it a "normal" one, local/global temporary table or table variable.